Two basic methods of analysis
are used in isotopic studies: decay counting and mass
spectrometry.

Decay counting methods are
used for fast-decaying radioactive isotopes. By measuring
the number of alpha or beta decays in a given period
of time and comparing with known decay rates, the abundance
of a radioactive isotope may be calculated.

Mass spectrometry measures
isotopic abundance by first ionizing each isotope, focusing
the resulting ions into a beam, and separating them
with a magnetic field according to the ratios of their
mass to net electric charge. It can be used for measuring
both stable and radioactive isotopes.